LTE (Long Term Evolution) systems are an evolution of the 3G (3rd Generation), which improves and enhances the air access technology of the 3G and uses OFDM (Orthogonal Frequency Division Multiplexing) and MIMO (Multiple Input Multiple Output) as a unique standard of the evolution of radio networks. Wherein, the LTE can provide a peak rate of downlink 100 Mbit/s and uplink 50 Mbit/s in a bandwidth of 20 MHz, which improves performance of cell edge users, expands cell capacity and lowers system delay.
There is not any relay node in existing LTE systems, the frame structure in a TDD mode in the LTE specification is shown in FIG. 1. For the frame structure of the LTE TDD, each 10 ms radio frame comprises two half-frames, and each half-frame comprises 51 ms subframes, wherein, each subframe can be divided into two 0.5 ms ordinary timeslots or three special timeslots DwPTS (Downlink Pilot Timeslot), and Guard Period GP and UpPTS (Uplink Pilot Timeslot) constitute a special subframe (S). In the existing specification, subframe 0 of the frame structure in the TDD mode is a downlink subframe, and the synchronization signal and the non-scheduling broadcasting signal of the radio frame are both in the subframe; considering the switching between the uplink and downlink, subframe 2 is in the uplink subframes.
Specifically, the two 5 ms half-frames in one radio frame can be two identical half-frame structures (that is, a frame structure with 5 ms as a period), in which, the configurations of uplink and downlink timeslots comprise: 1DL:3UL; 2DL:2UL; 3DL:1UL, and etc.
In addition, considering the utilization rate of radio resources and the compatibility among different frame structures, the two 5 ms half-frames can be different frame structures (that is, a frame structure with 10 ms as a period), and one of the half-frame structures has a special timeslot (S) of 1 ms, for the other half-frame structure, the 5 ms special timeslot can be flexibly configured as an uplink and downlink data timeslot, and in this frame structure, the configurations of uplink and downlink timeslots comprise: 6DL:3UL; 7DL:2UL; 8DL:1UL, 3DL:5UL, and etc. Configurations of uplink and downlink frame structures are shown in table 1.
TABLE 1uplink and downlink configurations of a TDD frame structurePeriod ofUplink anduplink anddownlinkdownlinkconfigu-switchingSubframe numberrationspoint012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
In an LTE-A system, an RN (Relay Node) will be introduced, which has features comprising, but not limited to, that: the RN, by controlling cells, make each cell be an independent cell and have an additional physical cell ID for the user equipment UE, and the RN will send information such as the synchronization channel and reference symbol, etc.
Currently, the introduction of the relay node renders three radio links of mobile communication systems based on a repeater: a direct link of eNB-macro UE, a backhaul link of eNB-RN, and an access link of RN-relay UE. Considering signal interference restriction in radio communication, the three links need to use orthogonal radio resources. As the transceiver of the relay node is in a TDD mode, the backhaul link and the access link occupy different timeslots in the TDD frame structure, but the direct link and the backhaul link can coexist, as long as their time frequency resources are orthogonal.
However, the current LTE specification does not define the transmission frame structure of the backhaul link between the eNB and the RN or related HARQ (Hybrid Auto Repeat Request) operation, and eNB and the RN cannot have effective and reliable communication in the backhaul link, thus it is necessary to define the transmission frame structure of the backhaul link and the related HARQ operation, so as to ensure the effectiveness and reliability of communication in the backhaul link.